[mergeinfo.py] Use remotes/origin/master instead of master

I don't have a local master branch, so those commands failed for me.

R=hablich@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2733923002
Cr-Commit-Position: refs/heads/master@{#43752}

tools/release/mergeinfo.py

@@ -25,10 +25,9 @@ def describe_commit(git_working_dir, hash_to_search, one_line=False):
 
 
 def get_followup_commits(git_working_dir, hash_to_search):
-  return git_execute(git_working_dir, ['log',
-                                       '--grep=' + hash_to_search,
-                                       GIT_OPTION_HASH_ONLY,
-                                       'master']).strip().splitlines()
+  cmd = ['log', '--grep=' + hash_to_search, GIT_OPTION_HASH_ONLY,
+         'remotes/origin/master'];
+  return git_execute(git_working_dir, cmd).strip().splitlines()
 
 def get_merge_commits(git_working_dir, hash_to_search):
   merges = get_related_commits_not_on_master(git_working_dir, hash_to_search)
@@ -45,7 +44,7 @@ def get_related_commits_not_on_master(git_working_dir, grep_command):
                                           GIT_OPTION_ONELINE,
                                           '--decorate',
                                           '--not',
-                                          'master',
+                                          'remotes/origin/master',
                                           GIT_OPTION_HASH_ONLY])
   return commits.splitlines()
 

tools/release/test_mergeinfo.py

@@ -30,12 +30,19 @@ class TestMergeInfo(unittest.TestCase):
       raise Exception(err)
     return output
 
+  def _update_origin(self):
+    # Fetch from origin to get/update the origin/master branch
+    self._execute_git(['fetch', 'origin'])
+
   def setUp(self):
     if path.exists(self.base_dir):
       shutil.rmtree(self.base_dir)
 
     check_call(["git", "init", self.base_dir])
 
+    # Add fake remote with name 'origin'
+    self._execute_git(['remote', 'add', 'origin', self.base_dir])
+
     # Initial commit
     message = '''Initial commit'''
 
@@ -68,6 +75,7 @@ class TestMergeInfo(unittest.TestCase):
 
   def _make_empty_commit(self, message):
     self._execute_git(["commit", "--allow-empty", "-m", message])
+    self._update_origin()
     return self._get_commits()[-1]
 
   def testCanDescribeCommit(self):